The present invention relates to a defrosting unit for a microwave oven, and more particularly to a defrosting unit equipped with a timer for selecting a cooking function or a defrosting function by simply manipulating a timer knob on the microwave oven having both the functions.
In the conventional art, a power selection switch, as shown in FIG. 1 (a), for cooking operation and a defrosting device, as shown in FIG. 1 (b), are separately provided in the microwave oven. The power selection switch for cooking comprises a sensitive switch 1, a cam 2 for on/off operation of the contact 1' of the switch 1, a plate spring 3 resiliently supporting the cam 2, and a main body 5, 5' supporting the spring 3 and a shaft, the external end of which mounting a knob 7 for turning in the directions of arrows 6 and 6'. On the other hand, the defrosting device in FIG. 1 (b) comprises a synchronous motor 8, a gear 10 mounted on the shaft 9 of the motor 8, a gear B11 engaging with the gear 10, a cam 12 for defrosting function and being mounted on a rotatory shaft 13, and a sensitive switch 14 for defrosting function and being mounted on a side of the cam 12.
For defrosting operation with the above construction, the knob 7 is turned in the direction of the arrow 6' for the cam 2 mounted in common with the knob 7 on a shaft 4 to follow in turn in the same direction 6'and turn off the contact 1' of the switch 1, as shown in FIG. 1 (a). On the other hand, the synchronous motor 8, with power on, rotates at a speed to turn the gear A10 mounted on the motor shaft 9 so as to drive the gear B11 in engagement with the gear A10 and in following rotate the cam 12 on the common shaft 13.
Consequently, the sensitive switch 14 comes to operate on/off in cycles of a period under the arcuate action of the cam 12 for defrosting operation.
Thus, for a defrosting operation, the switch 1 for cooking function is turned off while the switch 14 for defrosting function operates on/off in cycles.
For cooking operation, the knob 7 in the power selection switch in FIG. 1 (a) is turned in the direction of the arrow 6 contrary to the direction for the defrosting function so as to make the cam 2 follow in rotation in the same direction to turn on the contact 1' of the switch 1 for cooking, while the defrosting operation.
However, since the switch 1 is on for cooking function, the cooking operation of food proceeds irrelevant to the on/off operation of the switch 14 for defrosting.
In the above conventional construction having separate devices respectively for cooking and defrosting operations, a disadvantage is that the construction technically is complicated to result in a high manufacturing cost with a problem of difficulty in assembling.